Various methods exist for selective communication between a terminal and a plurality of other terminals in a network, in which the terminals are addressed by Internet protocol, including broadcasting and multicasting.
The most common type of IP communication is a unicast communication, that is to say, in which the communication is established between nodes whose individual addresses are identified in the datagrams transmitted. If a server is to send the same datagrams to more than one address, it must repeat the datagrams with each individual address. The unicast method of transmission is accordingly ill suited to mass distribution of messages or other communications to many destinations and is inapplicable if the IP address of the intended recipients is unknown to the sender.
To meet the requirement for transmitting Internet communications to many destinations, whose address may be unknown to the sender, a modified Internet protocol is available for multicast services. IP multicasting is the transmission of an IP datagram to a “host group”, a host or a set of hosts identified by a single IP destination address. A multicast datagram is delivered to all member terminals of its destination host group with the same “best-efforts” reliability as regular unicast IP datagrams, i.e., the datagram is not guaranteed to arrive intact at all members of the destination group or in the same order relative to other datagrams. The membership of a host group is dynamic; that is, hosts may join and leave groups at any time. An IP module may only receive datagrams if it has previously sent a request to join the group, specifying the group multicast address.
There is no restriction on the location or number of members in a host group. An incoming datagram destined to one of those groups is processed exactly the same way as datagrams destined to one of the host's individual addresses. Incoming datagrams destined to groups to which the host does not belong are identified by the group address and discarded without generating any error report or log entry.
Multicasting does not contain any mechanism for selection of the destination terminals by any criteria other than the addresses of the nodes that have registered membership of the host group and, in particular, does not offer the possibility of location-specific communication, that is to say, communication to nodes (terminals) having unspecified addresses within a chosen geographical area.
Patent specification WO 01/01718 “Location management for cellular systems” describes a method for determining a mobile station location based on information sent by the mobile terminal to the Regional Network Controllers (‘RNCs’). However, it does not disclose any method of communicating datagrams with numerous terminals selected according to chosen criteria, such as their geographical position.
Digital broadcasting, and in particular digital television, is another service enabling the transmission of programmes or other communications to many destinations over cable connections or satellite or terrestrial wireless electromagnetic transmissions. Broadcasting differs from IP transmission in that the communication is essentially unidirectional; if interaction is desired with the destination, the response of the destination must be through a different link, such as the Internet or telephony communications. Each transmission on a given channel reaches all receivers connected to that channel. While the coverage of broadcasting is inherently somewhat limited geographically, this does not enable selection of the destination terminals by chosen criteria and, in particular, does not offer the possibility of location-specific communication, that is to say, choosing the geographical area for the communication.
Data streams additional to the broadcast services may be transmitted over the same broadcast channels (‘encapsulated’). Patent specification WO 01/10081 describes a broadcast network for transmitting broadcast information and an event manager to add event information to the broadcast information. The event information either comprises information defining/identifying the specific end user device to which the event message is to be directed or does not contain any such information and is transmitted to all end user devices, without selection. In both cases, there is no selection of the end user devices by any criteria other than their addresses and, in particular, does not offer the possibility of location-specific communication, that is to say, communication to nodes (terminals) within a chosen geographical area.
International Patent Application WO 01/19029 describes a packet-switched network in which a routing means receives data packets from a sender and buffers data packets whose destination address is a multicast address of a multicast group. A control means designates filters for each receiver and/or for receiver-specific addresses determined by the control means, and supplies the determined addresses and designated filters to the routing means, which filters the multicast data packets and/of the determined addresses with the designated filters for each receiver of the multicast group and supplies the filtered multicast data packets to the filtered receiver addresses.
A need exists for a method enabling communication of datagrams over a communication network from one terminal to numerous other terminals selected according to criteria chosen as a function of information derived from the transmitting terminal.